DE69300146T2 - Method for regulating the speed of an internal combustion engine. - Google Patents

Description

BACKGROUND OF THE INVENTION Field of the invention

The present invention relates to a method for an isochronous PI control of the speed of an internal combustion engine during a gear shifting or gear shifting operation.

State of the art

For example, in a vehicle driven by an internal combustion engine and equipped with an electronically controlled automatic transmission system in which the operations of a gearshift and a clutch are controlled by means of a microcomputer to shift the gearshift to a desired gear position, it is necessary to synchronize the rotational speeds between two gears to be meshed in the transmission (Japanese Patent Application Publication No. Sho 60-179365). In order to establish such synchronization between the gears, isochronous control is usually used, and an amount of fuel to be supplied to an internal combustion engine is controlled by using PI control to bring the actual rotational speed of a gear into agreement with a desired target rotational speed of the same.

However, when the engine speed is controlled in the PI control mode, there arises a tendency of deteriorating the response characteristics of the control to achieve a variation of the target speed. In this case, the improvement in the response characteristics will impair control stability. In addition, an overshoot or undershoot state of the engine speed may be caused when the target speed fluctuates greatly for a short time. It can therefore be generally said that the PI control is unsuitable where the target speed is greatly different from the actual speed and it is necessary to make the actual speed equal to the target speed for a short time, for example, in the above example of synchronization control of the gear speed for the gear shifting operation of the above-mentioned transmission system.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a speed control method for an internal combustion engine with an isochronous PI control mode in which both the response characteristic and the stabilization characteristic can be satisfied at the same time, even if the target speed differs greatly from the actual speed.

According to the present invention, a method is provided for carrying out an isochronous PI control of the speed of an internal combustion engine during a gear shift, wherein a target position of a fuel regulating part for regulating the amount of fuel to be supplied to the engine is determined depending on a given target engine speed and an actual engine speed of the internal combustion engine. is calculated, the method comprising the following steps:

an initial value determination step is carried out to determine an initial value of an integral term for the isochronous PI control based on the difference between the target engine speed and the actual engine speed when it has been discriminated that the difference between the target engine speed and the actual engine speed is greater than a prescribed value, depending on a first discrimination step,

a second discrimination step is performed to discriminate whether or not the actual engine speed has been made substantially equal to the target engine speed by the isochronous PI control which is performed using the initial value determined in the step of determining the initial value,

and a step of changing the value of the integral expression to a value which corresponds to a value substantially equal to a no-load rack position of the fuel regulating part, at which an amount of fuel required to maintain the no-load rotation speed of the engine at the target engine rotation speed is supplied to the engine when it has been discriminated in the second discrimination step that the actual engine rotation speed is substantially equal to the target engine rotation speed.

Accordingly, when the difference between the target and actual engine speed reaches a value that causes problems with overshoot or undershoot due to, for example, a renewal of the target engine speed, the initial value of the integral term for PI control is determined based on the renewed target engine speed and the actual engine speed. The initial value can be determined so as to improve, for example, the response characteristic of the engine speed control. To achieve this, the initial value of the integral term should be determined so as to achieve the same effect as that obtained by increasing the gain of the PI control. This means that a large value should be selected as the initial value when an increase in the engine speed is required. On the other hand, a small value should be selected as the initial value when a decrease in the engine speed is required. When the actual engine speed becomes substantially equal to the target engine speed by the PI control using the value of the integral term determined above, the value of the integral term is changed to the value according to the no-load rack position, whereby large overshoot and undershoot can be effectively suppressed due to the fact that the torque for increasing or decreasing the engine speed becomes zero.

The invention can be better understood and other objects and advantages thereof will become more apparent from the following detailed description of preferred embodiments with reference to the drawings.

BRIEF EXPLANATION OF THE DRAWINGS

Fig. 1 is a schematic view illustrating an embodiment of a vehicle control system in which an engine speed is controlled according to the present invention;

Fig. 2 is a block diagram of the speed control unit shown in Fig. 1;

Fig. 3 is a flowchart of the execution of a speed control program in the speed control unit;

Fig. 4 is a detailed flow chart of a step for determining a value for an integral term for the PI control; and

Fig. 5 is a graph showing the characteristics of a minimum rack position and a no-load rack position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Fig. 1 is a schematic view showing an embodiment of a vehicle control system in which isochronous engine speed control is performed using a PI controller (hereinafter referred to as an isochronous PI controller) according to the present invention. In a vehicle control system 1 of Fig. 1, a diesel engine 2 is used to drive a vehicle (not shown), and fuel is supplied to the engine 2 from a fuel injection pump 3 equipped with a fuel regulating rack 4 for regulating the amount of fuel to be injected into the engine 2. Reference numeral 5 indicates a solenoid actuator for operating the fuel regulating rack 4. Further, a friction clutch 6 and a gear type transmission 7 are provided on the output side of the diesel engine 2, and a conventional automatic transmission system AT is formed by associating the clutch 6, the transmission 7 and a control unit 8 as described below.

The control unit 8 is equipped with a microcomputer and receives a set of position signals P sent from a position sensor (not shown) which is included in the transmission 7 and provides an indication of the current gear shift position of the transmission 7. The control unit 8 receives from the Sensor unit 9 receives an acceleration signal A indicative of the amount of depression of an accelerator pedal 10, a TDC pulse T indicative of when a piston in a predetermined cylinder (not shown) of the diesel engine 2 has reached its top dead center position, and a vehicle speed signal V indicative of the running speed of the vehicle driven by the diesel engine 2. A selector device 11 has a selector lever 11a for selecting a gear position of the transmission 7, and a selector position signal S indicative of the actual position of the selector lever 11a is generated from a sensor (not shown) associated with the selector lever 11a, which signal is sent to the control unit 8.

The control unit 8 is responsive to these input signals P, A, V and S and the input pulse T to perform the calculation required to execute the gear shift control and outputs a first control signal S1 to control the engagement/disengagement operation of the clutch 6 and outputs second and third control signals S2 and S3 to control the select and shift operations of the transmission 7, respectively. The transmission 7 is associated with a select actuator 12 responsive to the second control signal S2 to move the gear in a selected direction and a shift actuator 13 responsive to the third control signal S3 to move the gear in a shift direction. The first control signal S1 is applied to a clutch actuator 14 to operate the clutch 6. The operation to automatically shift the gear 7 to a desired position is carried out in a known manner depending on the control signals S1 to S3 generated by the control unit 3.

The vehicle control system 1 is equipped with an engine speed control system SS for electronically controlling the speed of the diesel engine 2 in addition to the automatic transmission system AT using the control unit 8. The engine speed control system SS has a speed control unit 21 which receives the acceleration signal A, the TDC pulse T, a rack position signal R indicating the position of the fuel control rack 4, and a vehicle speed signal V from the sensor unit 9.

As illustrated in Fig. 2, the speed control unit 21 is constituted by using a conventional microcomputer system including a central processing unit (CPU) 22, a read-only memory (ROM) 23, a random access memory (RAM) 24, an input/output interface (I/O) 25, and a bus 26 for connecting them. A control program for controlling the engine speed of the diesel engine 2 is stored in the ROM 23 in advance and is executed in the CPU 22 to generate a speed control signal CS which is applied to the solenoid actuator 5 to regulate the position of the fuel regulating rack 4.

As will be described later, the speed control unit 21 has not only a function of regulating the position of the fuel regulating rack 4 in accordance with a prescribed control characteristic in response to the operation of the accelerator pedal 10, but also has another function of regulating the engine speed to make the actual engine speed Na of the diesel engine 2 coincident with the target engine speed No requested at that time in an isochronous PI control mode according to the invention in response to a command signal I generated from the control unit 8. The command signal I serves to indicate that the transmission 7 performs a required gear shift operation.

An explanation will now be given of the engine speed control operation according to the speed control program stored in the ROM 23, with reference to Fig. 3. After the start of execution of the speed control program, the operation goes to step 31 where data based on the signals applied from the outside are input. Then, the operation moves to step 32 where the actual engine speed Na of the diesel engine 2 is calculated from the time interval between the TDC pulses T. At the next step 33 for determining a value of an integral term for an isochronous PI control operation, it is discriminated whether the command signal I has been generated from the control unit 8 or not, and the value of the integral term for the isochronous PI control according to the present invention is determined when the command signal I has been generated.

Referring to Fig. 4, when the operation advances from step 32 to step 51, it is discriminated at step 51 whether the level of the command signal I is equal to "1" or not or, in other words, whether the control for maintaining the rotational speed of the diesel engine 2 at a prescribed target value by means of an isochronous PI control operation is required or not. The decision at step 51 becomes NO if I = "0", that is, if the isochronous PI control is not required, and the operation advances to step 52, at which a flag UF indicating that the actual engine rotational speed should be increased and a flag DF indicating that the actual engine rotational speed should be decreased are cleared or set to zero. Then, the operation advances to step 34 (Fig. 3).

The decision at step 51 becomes YES when I = "1", that is, when the isochronous PI control is required, and the operation goes to step 53, at which the target engine speed No suitable for the operating state of the vehicle at that time is calculated in a conventional manner based on information from the sensor unit 9 and the control unit 8.

Thereafter, the operation proceeds to step 54 where a decision is made as to whether No - Na is greater than 200 rpm or not. The decision at step 54 becomes YES if No - Na is greater than 200 rpm, and the operation proceeds to step 55 where a decision is made as to whether the flag UF is "1" or not. The operation proceeds to step 34 if UF = "1". On the contrary, if UF = "0", the flag UF is set at step 56 and the operation proceeds to step 57 to calculate a no-load rack position defined as a position of the fuel control rack 4 according to an unloaded state at that engine speed. Then, the operation moves to step 58, where the calculated value of the no-load rack position is set as the value i of the integral term for the isochronous PI control, and the operation then goes to step 34. That is, the value of the no-load rack position is set as an initial value of the integral term when the target engine speed is greater than the actual engine speed by more than 200 rpm and the flag UF is "0". In this case, the value of the maximum rack position may be set as an initial value of the integral term to accelerate the increase in the engine speed.

On the other hand, if the decision at step 54 is NO, the operation moves to step 59 and it is decided at step 59 whether Na - No is greater than is greater than 200 rpm or not. The decision at step 59 becomes YES if Na - No is greater than 200 rpm, and the operation then proceeds to step 60. At step 60, discrimination is made as to whether DF is equal to "1" or not. If DF = "0", the decision at step becomes NO and the operation proceeds to step 61. Then, the flag DF is set at step 61 and the value i is set to zero at step 62. Thereafter, the operation proceeds to step 34. The operation proceeds to step 34 without executing steps 61 and 62 if the decision at step 60 is YES. That is, in the case where the actual machine speed is higher than the target machine speed by more than 200 rpm, the decision is made whether the flag DF is cleared or not, and the initial value of the integral term is set to zero when the flag DF is cleared.

If the discrimination at step 59 becomes NO, the operation moves to step 63, where discrimination is made as to whether the flag UF is set or not. The discrimination at step 63 becomes YES if UF = "1", and discrimination is made at step 64 as to whether No is smaller than Na or not. The operation moves to step 34 if it is discriminated at step 64 that No is larger than or equal to Na. On the other hand, in the case where No is smaller than Na, the operation moves to step 65, where the flags UF and DF are cleared and then steps 57 and 58 are executed.

If it is discriminated at step 63 that UF is equal to "0", the operation moves to step 66 where discrimination is made as to whether DF is set or not. The discrimination at step 66 becomes NO if DF = "0", and the operation then moves to step 34. On the other hand, the discrimination is made at step 66. Step 66 becomes YES if DF = "1", and the operation then moves to step 67, wherein discrimination is made as to whether No is greater than Na or not. If No is greater than Na, the discrimination at step 67 becomes YES and the operation then moves to step 65. On the other hand, if No is less than or equal to Na, the discrimination at step 67 becomes NO and the operation then moves to step 34. That is, in the case where the difference between No and Na is less than 200 rpm, it follows that the value of the no-load rack position is set as the value i of the integral term when UF = "1" and No is less than Na or when UF = "1" and No is greater than Na. In other words, the value of the no-load rack position is set as the value i of the integral term when the actual engine speed approaches the target engine speed and overruns the target engine speed.

Referring to Fig. 3, a decision is made at step 34 as to whether I = "1" or not. If I = "1", the operation proceeds to step 35, where the calculation for controlling the position of the fuel regulating rack 4 in the isochronous PI control is performed to obtain the target engine speed No by using the initial value set at step 33 to generate first target rack position data RD indicating the target position of the fuel regulating rack 4 for the isochronous PI control. The determination at step 34 becomes NO when the execution of the isochronous PI control is not requested and the operation then proceeds to step 42 where second target rack position data RL indicating the target position of the fuel regulating rack 4 for controlling the fuel regulating rack 4 in the case of using a minimum-maximum speed control characteristic is obtained according to the actual engine speed and the amount of operation of the accelerator pedal 10 is calculated. The operation then proceeds to step 40.

At step 36, discrimination is made as to whether the flag DF is set or not. If the discrimination at step 36 becomes YES when the flag DF is set, the operation moves to step 37. At step 37, a set of minimum rack position characteristics as illustrated in Fig. 5 is calculated, which includes the no-load rack position at the time when the rotation speed of the engine is equal to the target rotation speed No. At the next step 38, the minimum rack position RM according to the minimum rack position characteristics is compared with the rack position data RD.

The minimum rack position characteristic is defined as a characteristic indicating the minimum rack position required to prevent the occurrence of an overshoot condition in the case where the isochronous control is performed while the rack is positioned at its non-injection position until the actual engine speed becomes equal to the target engine speed, and then the value of the no-load rack position is set as the value of the integral term.

The determination at step 38 becomes NO when RM is greater than or equal to RD and the operation then moves to step 39 where the value of RM is set as the contents of the data RD. Then the operation moves to step 40. As described above, the occurrence of undershoot is effectively prevented by establishing the minimum rack position characteristics. On the other hand, when it is discriminated at step 38 that RM is smaller than RD, the discrimination at step 38 becomes YES and the operation moves to step 40 without executing step 39.

The maximum position of the fuel regulating rack 4 in the direction of increasing the fuel amount is calculated at step 40, and the rack position data obtained before step 40 is limited in such a manner that the data never indicates a position larger than the maximum position. The rack position control or fuel control is performed at step 41 by the speed control signal CS which is generated in accordance with the first or second target rack position data obtained in the manner described above. The operation then returns to step 31 after execution of step 41 and is terminated.

According to the arrangement described above, when the engine speed control of the internal combustion engine 2 is requested according to an isochronous PI control by the control unit 8, it is discriminated whether or not the difference between the target engine speed No and the actual engine speed Na is larger than a prescribed value, which can be appropriately determined (for example, 100 rpm is used in this embodiment), and the initial value of the integral term for the PI control is determined based on the result of the discrimination concerning the speed difference and the conditions of the flags DF, UF. When the actual engine speed becomes substantially equal to the target engine speed, due to the PI control including the integral term determined in the above-described manner, the value corresponding to the no-load rack position is set as the value i of the integral term, whereby the occurrence of a large overshoot or undershoot can be suppressed.

In order to ensure the desired response and stability characteristics, since the value i of the integral term is determined in relation to the difference between the actual and target engine speeds without correcting the target engine speed, no adjustment process for the PI control is required even if the conventional PI control mode is used for the engine speed control. As a result, a simple adjustment process can be realized and the controllability can be noticeably improved.

In this embodiment, the value of the no-load rack position is used as the value i of the integral term when the actual engine speed has become substantially equal to the target engine speed. However, a gradual change of the value i of the integral term for the PI control may be started before the time when the actual engine speed has become substantially equal to the target engine speed so that the value i of the integral term is made just equal to the value of the no-load rack position required for the engine speed at the time when the actual engine speed has just reached the target engine speed.

Claims (5)

1. Method for isochronous PI control of the speed of an internal combustion engine (2) during a gear shifting or gear shifting operation, in which a target position of a fuel regulating part (4) for regulating the amount of fuel to be supplied to the engine (2) is calculated depending on a given target engine speed (No) and an actual engine speed (Na) of the internal combustion engine (2), after which an initial value determination step is carried out to determine an initial value of an integral term for the isochronous PI control based on the difference (No-Na) between the target engine speed (No) and the actual engine speed (Na) when it is discriminated that the difference (No-Na) between the target engine speed (No) and the actual engine speed (Na) is larger than a prescribed value, depending on a first discrimination step, a second discrimination step is performed to discriminate whether or not the actual engine speed (Na) has been made substantially equal to the target engine speed (No) by the isochronous PI control which is performed using the initial value determined in the step of determining the initial value, and a step is carried out to change the value of the integral term to a value which corresponds to a value which is substantially equal to a no-load rack position of the fuel regulating part (4) at which a quantity of fuel which is required to maintain the speed of the engine (2) in the absence of a load at the target engine speed (No) is supplied to the engine (2) when second discrimination step, that the actual engine speed (Na) is substantially equal to the target engine speed (No). 2. A method according to claim 1, wherein the step of determining the initial value comprises a step of discriminating whether the target engine speed (No) is higher than the actual engine speed (Na) or not and a step of determining the initial value of the integral expression depending on whether the target engine speed (No) is higher than the actual engine speed (Na) or not. 3. A method according to claim 2, wherein the value of the no-load rack position is set as the initial value of the integral expression when the target engine speed (No) is higher than the actual engine speed (Na). 4. Method according to claim 2, according to which the initial value of the integral expression is set to zero if the target engine speed (No) is lower than the actual engine speed (Na) 5. A method according to claim 1, wherein in the event that the actual engine speed (Na) is higher than the target engine speed (No), minimum control position characteristics are calculated, the minimum control position characteristics indicating a relationship between the speed of the engine (2) and the minimum position of the fuel regulating member (4) in order to position the fuel regulating member (4) at a no-load rack position when the actual engine speed (Na) is made equal to the target engine speed (No), and whereupon the position of the fuel regulating member (4) is controlled so as not to become smaller than the minimum control position at any moment according to the minimum control position characteristics.